Ship Dimensions, Tonnage, and Buoyancy

Ship Dimensions and Length Measurements

• The basic dimensions of a ship include Length Overall (LOA).
• The length of a ship measured at the waterline is called Length at Waterline (LWL).
• The volume of a ship's hull is measured in cubic meters.

Displacement and Tonnage

• The displacement of a ship refers to the weight of the ship in water or the volume of water displaced by the ship.
• Gross tonnage represents the volume of all enclosed spaces in the ship.
• Net tonnage of a ship is the volume of all enclosed spaces minus the volume of the crew's quarters.

Archimedes' Law and Buoyancy

• Archimedes' Law states that the buoyant force exerted by a fluid on a submerged object equals the weight of the fluid displaced by the object.
• The formula for buoyant force is Fb = pgV.
• If the volume of the displaced fluid increases, the buoyant force increases.
• If the density of the fluid increases, the buoyant force increases.
• When a block of wood floats in water, the weight of the block of wood equals the buoyant force.

Stability and Center of Gravity

• A vessel is in stable condition if the metacentre is above the center of gravity.
• The formula in finding KM is KM = KG+GM.
• If KM is 10m and KG is 4m, then GM is 6 meters.
• If KM is 10m and GM is 6m, the center of gravity should be at 4 meters.
• If the metacentric height is 6m and the center of gravity is 4m, the height of the metacentre is 10 meters.
• If the height of metacentre is 10m and the center of buoyancy is 2m, BM is 8 meters.
• When the height of the metacentre is less than the height of the center of gravity, the vessel is in unstable equilibrium.
• When carrying a cargo of logs, loading the heaviest logs in the lower holds will minimize the effect of a tender vessel. Forward and Aft Drafts
• If forward draft is 0.81m and aft draft is 3.41m, the mean draft is 2.11 meters.
• If aft draft is 12.74m and forward draft is 12.66m, the trim is 0.08 meters.
• If aft draft is 13.68m and forward draft is 12.44m, the trim is 1.24 meters.
• If aft draft is 12.74m and forward draft is 12.66m, the mean draft is 12.6 meters.
• If forward draft is 3.41m and aft draft is 0.81m, the trim is 2.6 meters.

Stresses on a Ship

• The stresses that act along the length of the ship are called longitudinal stresses.
• The maximum longitudinal stress of a ship occurs at the midship section.
• The maximum torsional stress on a ship occurs at the waterline.
• Hogging is a longitudinal stress that causes the ship to bend upwards.
• Stresses in a ship are caused by the weight of the ship, the force of the waves, and the thrust of the propeller.
• Stresses in a ship are minimized by making the ship's hull stronger, distributing the weight evenly, and using a streamlined hull shape.
• A hydrostatic table provides data on the stability of the ship.

Hydrostatic Tables and Stability

• Displacement of a ship
• Draft of a ship
• Displacement of a ship is the weight of water displaced by a ship.
• A hydrostatic table is used to calculate the displacement of a ship.
• A hydrostatic table is usually tabulated in terms of draft of the ship.
• The metacentric height of a ship is the distance between the metacentre and the center of gravity.
• The hydrostatic table is used by the ship's captain to calculate the stability of the ship.
• The curve of Statical Stability is a plot of the righting arm (GZ) against the angle of heel.
• The maximum righting arm (GZ) occurs at the Angle of heel.
• The area under the curve of Statical Stability gives the amount of energy the ship can absorb from external heeling forces.

Material Properties and Ship Dimensions

• The ultimate strength is the stress at which the material breaks.
• Strain is the change in length of a material divided by its original length.
• The stress-strain curve plots stress against strain.
• The term referring to the distance between the forward and aft perpendicular of a ship is Length Overall (LOA).
• The beam of the ship is its width at its widest point.
• The term describes the vertical distance from the waterline to the continuous deck is freeboard.
• The term draft of a ship refers to the depth of the ship's hull below the waterline.
• The keel of a ship is the lowest part of the ship's hull, running along the centerline.
• The length between perpendicular refers to the length between the forward and aft perpendiculars.